Oscillation generator



20,1943; 7 L. A.:MEACHAM 2,43 ,669

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5 Sheets-Sheet 5 Original Filed Oct. 5, 1943 K UU uwwmvih lNl/ENTOR By L. A. MEACHAM NQQ ATTORNEY Patented Jan. 20, 1948 OSCILLATION GENERATOR Larned A. Meacham, Summit, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Original application October 5, 1943, Serial No. 505,024. Divided and this application January 31, 1945, Serial No. 575,449

6 Claims. (01. 250-436 This invention relates to electric wave generating apparatus and particularly to an oscillation generator which is adapted for use in an electrical range or distance indicating system.

This application is a division of application Serial No. 505,024, filed October 5, 1943 (United States Patent No. 2,422,205, June 1'7, 1947).

In a specific embodiment of the invention herein shown and described for the purpose of illustration, recurrent pulses of energy are radia ated to an object, echo pulses are received from the object, and an indication of the distance from the pulse radiator and receiver to the object is produced. To produce this distance indication, means are provided for generating range pulses which are delayed with respect to corresponding reference pulses by an amount equal to the delay between the radiated pulses and the corresponding echo pulses. There is provided a range indicator which is preferably calibrated to indicate the distance to the object directly, a delay of one microsecond between a radiated pulse and its received echo corresponding to a distance of 164 yards, approximately. A range indicating apparatus of this general type is disclosed in my copending application Serial No. 491,791, filed June 22, 1943 (United States Patent No. 2,422,204, June 17, 1947) but the apparatus described in this application is in some respects an improvement thereover. Portions of the range indicating apparatus shown and described herein may obviously be substituted for corresponding portions of the range indicating apparatus shown and described in said copending application. There is employed a start-stop circuit, similar to the start-stop circuit of said copending application, upon which are impressed pulses in synchronism with the radiated pulses for causing the generation of a square voltage wave. This wave has a negative portion starting with the pulse impressed upon the circuit, which portion has a duration equal to or preferably greater than the maximum delay occurring between the time of radiation of a pulse and the time of reception of an echo of the radiated pulse. This negative portion is followed by a positive portion which occupies a time interval during which the circuit is returned to its stable waiting condition ready to be started again by a succeeding pulse. A timing wave generator comprising an antiresonant circuit is started due to the abrupt decrease in potential at the start of the negative portion of the wave from the start-stop circuit and the timing wave is quickly quenched due to the positive portion of the start-stop wave. Two triode electronic devices having their anode-cathode paths in series with the antiresonant circuit are provided for alternately abruptly interrupting and starting the flow of current through the antiresonant circuit in response to the square wave from the start-stop circuit impressed upon the control electrodes of the triodes simultaneously. A feed: back path is provided for maintaining the output voltage of the generator at constant amplitude. A phase shifter is provided for continuously shifting in either direction, the phase of the wave from the timing wave generator. The phase shifter comprises an improved wave generating circuit which produces, under control of the timing wave, two voltage waves which are accurately in quadrature and which start coincidently with each timing wave train. prolonged starting transient, such as is produced by a simple resistance-capacity phase splitter, is thus avoided. The wave generator employs an electronic device having a high mutual conductarms and such an arrangement of related impedance elements in its anode-cathode circuit that, when a varying potential is impressed upon its control electrode, there are produced at the anode and cathode, respectively, potential waves one of which is proportional to the derivative of the other, that at the cathode being an accurate copy of the impressed potential. When the timing wave applied to the control electrode is sinusoidal and has an initial phase such that there is no abrupt change in instantaneous potential, there is preferably employed a path comprising induct.- ance and resistance in shunt with respect to each other between the anode and a source of anode current and a path comprising capacitance shunted by resistance between the cathode and the current source, the first-mentioned resistance being equal to the capacitive reactance and the second-mentioned resistance being equal to the inductive reactance. The phase shifting circuit also comprises a phase shifter condenser, similar to the phase shifting condenser of said copending application. The timing wave from the phase shifting circuit is amplified and the amplified wave supplied to a pulse generator which produces a series of alternately positive and negative sharp pulses which are accurately spaced by a predetermined interval.

, A pulse selector is provided for generating a pulse which is coincident with a desired one of each group of timing pulses. This pulse selector makes use of a circuit having resistance R and capacitance C of fixed time constant, the charg- The production of a 3 ing of the capacitance being initiated in response to the wave front of each negative portion of the square wave from the start-stop circuit. There is provided an electronic device having a plurality of electrodes comprising a cathode, a control electrode and an anode, which device is normally non-conducting and which is made conducting coincidently with one of the timing pulses to cause a selected timing pulse to be generated. The exponentially rising potential due to the charging of the condenser is applied to the control electrode, there is applied to the cathode a potential which is varied by means of a potentiometer, and the timing pulses are superposed on one of these potentials. One of the timing pulses will thus bring the control grid to a sufiiciently high potential with respect to the cathode potential to cause anode current to flow and a range pulse to be produced at the anode, the time of selection of a timing pulse to form a range pulse varying in accordance with the setting of the potentiometer which controls the cathode potential. The resistance of the potentiometer is nonuniformly distributed to correct for the nonlinearity of the potential rise due to the charging of the condenser and the potentiometer shaft is geared to the shaft of a phase shifting condenser in the phase shifter so that the delay between the radiated pulse and the selected timing pulse may be varied continuously.

The range indicating apparatus has a small minimum delay, say about one microsecond. A fixed delay circuit, the delay of which is equal to or greater than this minimum delay of the range unit is preferably included in the radio receiver so that when the transmitted pulses are directly impressed upon the receiver, the resulting pulses from the receiver may be made coincident with the corresponding range pulses from the range unit when the range indicator is set for zero distance. The range pulses are impressed upon one plate and the echo pulses are impressed upon the other plate of a pair of deflecting plates of a cathode ray tube, a linear sweep wave being applied to another pair of deflecting plates for deflecting the cathode ray beam perpendicularly with respect to the deflection due to the field set up by the first pair of plates. To determine the range of an object, the delay of the range unit is varied unil the visible indication due to the range pulses on the screen of the cathode ray tube is in alignment with the indication on the screen due to the echo pulses from the radio receiver. The range of the object from which the echoes are received may then be read on the indicator of the range unit.

If desired, the range pulses which are brought into coincidence with the echo pulses for causing a range indication to be produced may be used together with the echo pulses to control apparatus for automatically controlling the phase shifting condenser and potentiometer of the range indicator to maintain the range pulses and the echo pulses in synchronism. An apparatus of this type is disclosed in a copending application of B. M. Oliver, Serial No. 491,829, filed June 22, 1943.

The invention will now be described with reference to the accompanying drawing in which:

Fig, 1 is a block diagram of a ranging system in accordance with the present invention;

Fig. 2 consists of curves to which reference will be made in describing the invention; I

Figs. 3, 4 and 5, when Fig. 3 is placed to the left of Fig. 4 and Fig. 5 is placed to the right of Fig. 4, are a schematic view of a range indicator in accordance with the present invention; and

Figs. 6 to 9, inclusive, are diagrams to which reference will be made in describing the invention.

Referring now particularly to Figs. 1 and 2, there is disclosed a range indicating system in which recurring brief pulses of high frequency electromagnetic wave energy are produced by a transmitter IE! and radiated from a directional antenna ll toward an object the distance of which is to be determined and in which the wave pulses reflected from the object are received by antenna l2 and detected by a radio receiver l3. An oscillator l4 produces a sinusoidal wave having a period somewhat longer than the time required for a radio wave to travel twice the maximumdistance to be measured. Starting pulse generator 15 produces pulses as indicated at a, Fig. 2, at regular intervals, one for each cycle of the sine wave from oscillator M. It is not essential to the operation of the system, however, that these pulses occur at regular intervals. The starting pulses a which are of very brief duration, say one-quarter miscrosecond, key the radio transmitter ill to cause the radiation of corresponding pulses b of high frequency radio energy. The starting pulse generator l5 and radio transmitter I0 may be the same as the impulse generator and radio transmitter described in my copending application supra. The starting pulses a are also impressed upon a range indicator l9 to produce output or range pulses i which are delayed by a desired amount with respect to the starting pulses a. The range indicator has a small fixed minimum delay, about one microsecend, and a delay circuit having a, delay at least equal to this minimum delay is preferably included in the radio receiver l3 so that the pulses 7 from the receiver and the corresponding range pulses i from the range unit may be adjusted to be coincident when the transmitted pulses b are directly impressed upon the radio receiver I3, and when the range indicator is set for zero distance.

The starting pulses a are impressed upon a start-stop circuit [6 of the range unit for generating a square voltage wave 0 having an initial negative portion l1 starting coincidently with a startin pulse a and a positive portion I8. The intervals during which the negative portions I! of wave 0 occur mark the active periods of the range indicating apparatus and the intervals during which the positive portions [8 occur mark the quiescent periods of the apparatus when in operation. These active periods remain fixed while the quiescent periods may vary with frequency variations of source l4 within a limited range.

The voltage wave 0 produced by the start-sun) circuit is impressed upon a timing wave generator 293 which generates a succession of trains of constant frequency oscillatory waves d the phase of which may be shifted continuously through a plurality of cycles by turning the handle I26 of a phase shifter 2 l. The phase shifted timing wave, indicated at e of Fig. 2, starts with an abrupt departure from zero to whatever initial instantaneous amplitude corresponds to its phase position. The period of this oscillatory wave, Or a phase shift of the wave through a single cycle, corresponds to the time interval required for a radiated wave to travel through a certain distance and for its echo to return through that distance. The'distance represented by a single cycle of the oscillatory wave is the velocity of ropagation of the radiated pulse divided by twice the frequency of the oscillatory wave. The timing wave 6 from the output amplifier of the phase shifter 2| is impressed upon a timing pulse generator 22 which produces alternate positive and negative timing pulses f, a pulse being produced at the beginning of each half cycle of the timing wave. The square wave from the start-stop circuit and the timing pulses 7 from the timing pulse generator are impressed upon a pulse selector 23 which selects one of the timing pulses 26 of each group of timing pulses which is delayed by a desired interval with respect to the corresponding starting pulse a, as shown at 2, Fig. 2. As indicated at g in Fig. 2, an exponentially rising potential 36 having the timing pulses f superposed thereon is impressed upon a control electrode of an electronic device and a potential 31 which may be varied by means of a potentiometer is impressed upon the cathode of the electronic device to cause the selection of a pulse 26 which causes the control electrode potential to increase sufficiently with respect to the cathode poi tential to cause the flow of anode current through the electronic device. The shaft 34 of the potentiometer of the pulse selector 23 is connected through the gears 24 to the shaft 29 of a phase shifting condenser of the phase shifter 2| so that the change in cathode potential 31 is equal to the change in peak potential of a superposed timing pulse, such as pulse 26, due to the phase shift of the timing pulses, the resistance of the potentiometer being tapered to correct for the curvature of the exponentially rising potential 36. Only one pulse of each group of timing pulses appears at the output of the pulse selector 23, the pulses of each group which follow a selected pulse being blocked by the output amplifier of the pulse selector.

The echo pulsesa are impressed upon one of the vertical deflecting plates 3| of a cathode ray tube 30 and the range pulses i are impressed upon the other vertical deflecting plate. If desired, of course, a step pulse may be produced under control of the selected pulse 1' and impressed upon a vertical deflecting plate of the cathode ray tube for producing a range mark on the cathode ray tube screen as disclosed in my copending application, supra. Any suitable linear sweep wave h may be impressed upon the horizontal deflecting plates of the cathode ray tube 35. As shown, the sweep wave generator 35 is controlled by the starting pulses a from starting-pulse generator I to maintain the sweep wave in synchronism with the starting pulses. Alternatively the pulsesz' could be utilized for controlling the sweep wave generator and pulses which are delayed by a short fixed period with respect to the pulses i could be used as the range pulses impressed upon a vertical deflecting plate of the cathode ray tube. By rotating shaft 29 of the phase shifter condenser to which the potentiometer of the pulse selector is geared, a range mark produced by range pulses i may be caused to travel across the luminescent screen of the cathode ray tube until it is brought into alignment with an echo mark produced by echo pulses :i. The distance to the object from which the echo pulses are received may then be read directly from a revolution counter or range indicator 32 attached to shaft 29.

The range indicating apparatus is shown in greater detail in Figs. 3, 4 and 5 when Fig. 3 is placed to the left of Fig. 4 and Fig. 5 is placed to the right of Fig. 4. A suitable starting pulse generator and radio transmitter are shown in my 'copend-ing application supra and are therefore not being described in detail herein. The startst'op circuit l6 is similar to the start-stop circuit described in said copending application but is designed to prevent the false triggering of the circuit by extraneous pulses of smaller amplitude than that of the starting pulses a. The startstop circuit employs two electronic triodes VLI and V91, triode V|.| having a cathode 4|, a control electrode 42, and an anode 43 and triode V9.| havinga-cathode-44, a control electrode 45 and an anode 46. Negative starting pulses a. from the starting pulse generator H: are applied through a 50-micromicrofarad condenser Cl across 0.5- megohm resistor RI which is connected between the control electrode 42 and the grounded cathode 4|. The anode 43 is directly conductively connected to the control electrode 45 and the anode-46 is connected 'to the control grid 42 through a condenser C4 the capacity of which is 400 micromicrofarads when a maximum range of 22,000 yards is to be measured. For this range the alternating current source I4 may have any frequency up to about 4,000 cycles. The cathode 4-4 is connected to ground through 15,000-ohm resistor R4 shunted by a -500-micromicrofarad con-denser C6. A-node potential is supplied to the anode 43 from the positive terminal of 300-volt battery 5| through series resistors R8 (1,000 ohms) and 0.1-megohm resistor R3, the negative battery terminal being grounded. Positive volt age from source 5| is supplied to anode 46 through series resistors R8, R1 (18,000 ohms) and RB (18,000 ohms). The positive battery terminal is also connected through series resistors R8 and R5 (56,000 ohms) to the cathode 44. A 50-micromicrofarad condenser C5 is connected in shunt with respect to resistor R6. A filter condenser C81 of 0.1 microfarad is connected between the negative terminal of resistor R8 and ground. A resistor R86 of 1.8 megohms is connected between the negative terminal of resistor R8 and control grid '42 to maintain the grid positive with respect to cathode 4| during quiescent periods and thus to lower the input impedance and prevent false operation of the circuit due to extraneous pulses during this period. The negative pulse a applied to the control grid 42 causes the interruption of anode current in triode V|.|, to make the potential at anode 43 and at control grid 45 more positive. Anode current is thus caused to flow in triode V9.|. Triode V|.| continues to be cut off and V9.| continues to be conducting during the active period due to the discharge current of condenser C4 flowing through the anodecathode path of triode V9.| and resistor RI and the resulting negative bias on the control grid 42. At the end of the active period, this discharge current and the resulting grid bias reach a sufficiently low value to cause the triode V|.| to pass anode current and during the following quiescent period the condenser C4 is again charged through resistors R6 and R1 and the control electrode-cathode path of triode V|.|'. When the triode V9.| becomes conducting, the potential at the common terminal of resistors R6 and R1 becomes less positive with respect to ground and, when the conduction through triode V9.| is interrupted the common terminal of resistor R5 and R1 becomes more positive, thus producing the start-stop wave 0.

The start-stop wave 0 from the start-stop circuit is impressed upon the input circuits of triodes V2.I and V2.2 of the timing wave generator 20. The common terminal of resistance R6 and R! is connected through 0.01-microfarad condenser Cl and 0.0l-microfarad condenser C9, to the control electrode of triode V2.2 which is connected through l-megohm resistor RN to the grounded cathode. The common terminal of resistors R and R1 is also connected through condenser Cl and 0.01-microfarad condenser CID to the control electrode of triode V2.I which is connected through l-megohm resistor R9 to the cathode. The anode current paths for triodes V2.I and V2.2 may be traced from the positive 300-volt terminal through resistor R8, 10,000- ohm resistor Rl'il, the anode-cathode path of triode V2.I, the antiresonant circuit comprising 3.66-millihenry inductor L2 shunted by 1,000- micromicrofarad condenser CI3 and the anodecathode path of triode V2.2 to ground. The anode-cathode path of tube V2.2 is shunted by 25- micromicrofarad variable condenser CM. Condenser C82 of 0.1 microfarad is connected between the cathode of triode V2.I and ground. The inductance L2 and the condenser CI3 are enclosed within a grounded shield 53. This shielded antiresonant circuit is placed in a suitable oven (not shown) the temperature of which is maintained constant in order to avoid frequency variations due to temperature change. During each quiescent period a current of about milliamperes flows in the anode current circuit of triodes V2.I and V2.2, the voltage drop across each of the anode-cathode paths of these tubes and that across resistor RH] being about 100 volts. The interruption of the anode current from the 300- volt source due to the negative portion I! of the start-stop wave impressed upon the control grids of triodes V2.I and V2.2 simultaneously starts the oscillatory timing wave d in the circuit. The oscillatory wave is quenched during the early portion of the quiescent period due to the positive portion is of the start-stop wave applied to the control grids of triodes V2.I' and V2.2. The frequency of the timing wave is 81.955 kilocycles which corresponds to a range of 2,000 yards per cycle. When anode current is flowing in the circuit, condenser C82 is charged to about 100 volts and this charge is maintained during the active periods of the range indicator when the triodes V21 and V2.2 are non-conducting. Control of the current by the twotriodes, acting simultaneously, results in keeping the potential across C82 or between the upper end of L2 and, ground constant at all times.

In order that succeeding stages of the range unit may behave uniformly throughout the active period, the timing wave is sustained at constant amplitude by means of a positive feedback which is conveniently provided through the cathode follower action of the electronic device V3 of the phase shifter circuit, as will be described below. The anode-cathode circuit of this tube may be traced from the 300-vo1t source through 1,000- ohm resistor R24, inductor L! of 11.64 millihenries in parallel with 6,000-ohm resistor RII, the anode-cathode path, 10,000-ohm resistor RIB in parallel with 250-micromicrofarad condenser CI5 and l00-rnicrolnicrofarad variable condenser CIB, to ground. The anode of triode V2.2 is connected through 100-ohm resistor RIB to the con trol electrode and a mid-tap of inductor L2 is connected through 47,000ohm resistor RIG to the cathode. Screen grid potential is supplied to the tube through 20,000-ohm resistor RI9 and 100-ohm resistor RIB with the common terminal of RIB and RIB connected to the cathode through 0.1-microfarad condenser CH. The tube V3 has a high mutual conductance and the impedance between the cathode of V3 and ground is sufflciently high to cause the alternating component of the potential at the cathode with respect to ground to be an accurate copy of the potential at the control grid with respect to ground. The steady state impedance of the antiresonant circuit CI3, L2, is about 200,000 ohms and is essentially resistive at its natural frequency. The impedance looking in at the mid-tap of inductance coil L2 is one-quarter of this value or approximately 50,000 ohms. Accordingly, if RM is matched to this approximately 50,000-ohm impedance, one-half of the cathode voltage will be impressed across the upper half of the coil L2 (the upper terminal being connected through condenser C82 to ground). Due to the autotransformer action between the upper half of coil L2 and the entire coil, the voltage at the lower terminal will be double that at the mid-tap of coil L2. In other words, a voltage equal to the cathode voltage is impressed upon the grid and the net gain of the feedback path is equal to unity and, when this condition exists, no rapid increase or decrease in amplitude of the timing wave can occur. The resistance of resistor RM may be varied until this unity gain is obtained. Since the timing wave is interrupted after about 11 cycle have been generated, a small departure from unity gain of the feedback path would not cause an appreciable change in amplitude.

The use of tube V3 and its associated circuit to provide feedback for the oscillatory circuit CI3, L2, is a secondary one. The primary purpose of this circuit is to generate two waves of substantially equal amplitude which are accurately in quadrature with respect to each other starting substantially at the first instant of each wave train. A starting transient, lasting through a considerable fraction of a cycle of the timing wave, such as is produced with a simple resistance-capacity phase splitting circuit, is thus avoided.

The method of obtaining the quadrature voltages will be explained with reference to Figs. 6, 7, 8 and 9, each of which shows the cathode, control electrode and anode of electric discharge device V3. The curves in each figure show the alternating component of the cathode potential Ex, which is substantially the same as the grid potential Ed, the current I through the anodecathode path and the anode potential EP, all potentials being with respect to ground. In Fig. 9 the two components of current I, namely, I0 and IR are also shown.

In Fig. 6 a resistance R is connected between the anode and the positive terminal of the anode voltage source (+B), the negative terminal of the anode voltage source being grounded in each case., A capacitance C is connected between the cathode and ground. The time to is the instant at which the current in the circuit of inductance L2 is interrupted to start the generation of the timing wave, The timing wave potential is impressed upon the grid in each case and it is assumed that the electronic tube has a mutual conductance so large that the dilrerence between the grid potential EG and the cathode potential Ex is negligible. The current in the circuit is That is, EP is proportional to the derivative of Ex. In the absence of tube overloading, this relationship is true for both the steady-state timing wave and the discontinuity at time to. If in the steady state amplitude of the anode the cathode potential In order to make the potential wave equal to wave, R is made equal to L wC so that Then EP and EK are thus equal in amplitude but 90 degrees out of phase with respect to each other. This arrangement of Fig. 6 suffers from the fact that no unidirectional space current can how in the circuit because the cathode i connected to ground only through a condenser. This difliculty can be obviated by connecting a high resistance or a high inductance path across the condenser C but such a modified circuit would cause the introduction of some phase error.

In the arrangement illustrated in Fig. 7, an inductance L is connected between the positive terminal of the unidirectional voltage source +3 and the anode, and a resistance R is connected between the cathode and ground. In this case .llr R and d1 Q dEK If, as before EK=A sin wt EB: LAco;OS wt and if R=wL, Er: A cos wt. As before, EP and Ex are in quadrature and EP is proportional to the derivative of Ex. In this embodiment there is the practical difficulty that the sudden rise of voltage across the inductance shock-excites it in antirescnance with its stray capacitance and this results is objectionable irregularities in the wave shape.

In the arrangement illustrated in Fig. 8 a resistance R is connected between the anode and a positive terminal of the direct voltage source and an inductance L is connected between the cathode and ground. In this case the current Fig. 8, the constant in these expressions acquires a positive value equal to the. peak value of the alternating component of current. The current starts up from zero as though from a negative peak in its cycle. If the current were to continue as a pure sinusoidal wave, an increased average current would be required. Since there is no change in the steady-state potentials on the tube electrodes to sustain an increased current, the average value of the current wave returns to its original value exponentially with a time constant which may be shown to be equal to L multiplied by the mutual conductance of the tube.

It should be noted that if the timing wave potential at the grid and cathode were to start a quarter cycle earlier or later, that is, with an abrupt rise or fall of potential to maximum or minimum peak amplitude, the arrangement of Fig. 8 would become feasible because the constant of integration would equal zero, and the arrangements of Figs. 6 and 7 would acquire transient difiiculties in that differentiation of the steep wave front would tend .to produce tube overload- The arrangements of Figs. 6 and 7 can be combined as shown in Fig. 9 so that the inductance L and resistance RP in shunt with respect to each other are connected between the anode and the positive terminal of the direct voltage source and resistance RK and capacitance C in shunt with respect to each other are connected between the cathode and ground. This is the arrangement which is specifically utilized in the range unit of Figs. 3, 4 and 5. In this case, if the current IRP through RP equals the current Io through C and if the current In through L equals the current IRK through Rx If, as before then EP=-A cos wt.

In this embodiment resistance R1: provides a direct current path from the cathode to ground and resistance RP critically damps the undesired oscillations which would be generated due to the shock-excitation of the inductance L if the damping were omitted. In the circuit arrangement shown in Fig. 3, the cathode resistance R1; is made up effectively of resistors Rl5, RI!) and twice the resistance of RM, all in parallel, since each is in an alternating current path between the cathode and ground. Twice the resistance of RM is efiectively in the circuit because of the impedance of the tuned circuit L2, C13. The screen grid capacitor CIT is returned to the oathode in order that the same alternating current may flow through the anode and cathode impedances. The cathode potential of tube V3 is such with respect to the control grid potential that the grid current is zero at all times. By variation of trimmer condenser CIB in the cathode circuit, it is readily possible to adjust the cathode and anode voltages to exact quadrature. The amplitude of these voltages are then equal if the inductance of LI has the correct value in relation to the plate and cathode resistances.

In some cases it may be desirable to employ a continuous wave rather than an intermittent wave for the control grid potential Ed in which case no difiiculty will be experienced due to parasitic oscillations or starting transients as discussed above in connection with Figs. '7 and 8. Moreover, it may be desirable in some cases to employ a potential Wave EG other than a sine wave. When any variable potential is impressed upon the control electrode, there will be produced at the cathode and anode electrodes, respectively, varying potentials one of which is proportional to the derivative of the other, within the obvious limitations imposed by stray capacitances, tube overloading, and the constant of integration in the case of the circuit of Fig. 8.

There are provided two phase inverter triodes V4.! and V4.2 each for impressing upon opposite sector stator plates of a phase shift condenser C25 timing wave potentials which are 180 degrees out of phase with respect to each other. The anode current path for triode V4.l may be traced from 300-volt source through resistor R24, 10,000-ohm resistor R23, the anode-cathode path, 1,500-ohm resistor R22 and 10,000-ohm resistor R2! to ground. The control grid of this triode is connected through l-megohm resistor R29 to the common terminal of resistors R2! and R22. The anode current path for triode V4.2 may similarly be traced from the 300-volt source through resistor R24, 10,000-ohm resistor R28, the anode-- cathode path, 1,500-ohm resistor R27, and 10,000-- ohm resistor R25 to ground. One-megohm resistor R26 connects the control grid to the common terminal of resistors R2! and R25. A 0.1- microfarad condenser C83 provides a W impedance path from the negative terminal of resist-or R24 to ground. The cathode of tube V3 is connected through 0.01-microfarad condenser GM to the control grid of triode V4.! and the anode of tube V3 is connected through 0.01-microfarad condenser Cl9 to the control grid of triode V3.2.

The mutual conductance of each of the triodes V4.! and V4.2 is sufiiciently large to cause the cathode potential of each to be an accurate copy of the potential of the corresponding control electrode. As the same current passes through R23, and RZI, by way of the anode-cathode path of V4.!, the anode potential of V4.! is equal in am plitude to the potential at the junction of R2! and R22, but 180 degrees out of phase therewith. Sim larly, amplitude to, but 180 degrees out of phase with, the potential at the junction of R25 and R27. In View of the phase relationship established in the circuit of V3, it may be seen that the four last-mentioned potentials are alike in amplitude, but that three of them difier in phase from the fourth by 90 degrees, 180 degrees and 270 degrees, respectively, this relationship being established at essentially the first instant of each timing wave train.

The phase shifter condenser C25 comprises a metallic ring 86, four metallic stator sectors 8!, 82, 83 and 84 and a dielectric rotor 81 of a material having a dielectric constant considerably different from that of ir. The phase shifter condenser is described in detail in my copending application, supra. The stator sector 8! is connected to the common terminal of resistor R23 and the anode of tube 4.!; stator sector 83 is connected to the common terminal of resistors R2! and R22; stator sector 82 is connected to the common terminal of resistor R28 and the anode of tube 4.2,

and stator sector 84 is connected to the common terminal of resistors R25 and R21. Condensers C23 and C24 each of 10 micromicrofarads are connected between stator sectors 8| and 82, re-

the anode potential of V4.2 is equal in 12 spectively, and ground. Variable 25-micromicrofarad condensers C2! and C22 are connected between stator sectors 83 and 84, respectively, and ground, these condensers being variable to allow for accurate balancing of the cathode and anode reactances.

The ring stator 88 of the phase shifter is connected by lead 49 to the input of a two-stage amplifier comprising electronic tubes V5 and V6 and the output of the amplifier is connected to a timing pulse generator circuit comprising electronic tubes V1 and V8. 'The lead 49 is connected through 100-ohm resistor R33 to the control grid of the tube V5. Anode potential is sup plied to the tube from 300-volt source 5| through 1,000-ohm resistor R36 and 10,000-ohm resistor R35, the anode-cathode path, 180-ohm resistor R32 and LOGO-ohm resistor R3! to ground. Control grid biasing potential is provided due to anode current flowing through resistor R32, which bias is applied to the grid through 0.1- megohm resistor R29 and 0.47-megohm res stor R30 in series. A 0.01-microfarad condenser C2! connected from the common terminal of resistors R29 and R30 to'the cathode of tube V5 by-passes alternating components of the voltage across R32. Screen grid voltage is supplied to tube V5 through resistor R36, 68,000-ohm resistor R3! and IOU-ohm resistor R34, the common terminal of resistors R3! and R34 being connected through -0.01-microfarad condenser C29 to the cathode. Condenser C26 of 0.1 microfarad is connected between ground and one terminal of resistor R36 to suppress voltage variations of the 300-volt source. The anode of V5 is connected through 0.01-microfarad condenser C28 and 100-ohm re sistor R to the control grid of amplifier tube V6. Anode volta e is sup lied to tube V6 from the 300-volt source through resistor R36, 10,000- ohm resistor R43, the anode-cathode path and 180-ohm res stor R4! to ground. A 0.1-megohm res stor R38 is connected from the common terminal of condenser C28 and resistor R40 to ground. Screen grid voltage is supplied from the 300-volt source through resistor R36. 68.000-ohm resistor R44 and IOU-ohm resistor R42. the common terminal of resistors R44 and R42 being connected through 0.01-microfarad condenser C3! to the cathode. Negative feedback is provided by connecting the anode of tube V5 through 0.1- megohm resistor R39 to the cathode of tube V5.

The amplified timing wave voltage at the anode of tube V5 is impressed through 0.01-microfarad condenser C39 and 100-ohm resistor R45 upon the control grid of'the center clipper tube V! of the timing pulse generator 22. The common terminal of resist-or R46 and condenser C36 is connected through 0.1-megohm resistor R45 to ground and the tube cathode is connected through 10,000-ohm resistor R4! shunted by 50-micromicrofarad condenser C33 to ground. Anode voltage is supplied to tube V! from the 300-volt source through LOGO-ohm resistor R53 and 18,000- ohm resistor R49. and screen grid voltage is applied through -ohm resistor R50 from the voltage divider formed by 33,000-ohm resistor R5! and 33,000-ohm resistor R52. the common terminal of resistors R5! and R52 being connected through l-microfarad condenser C34 to the oathode. Tube V'! acts as a cathode follower during the positive half cycles of the timing wave impressed upon its grid and is cut off during the negative half cycles. During the positive half cycles on the grid, when the grid potential first increases and then decreases, the anode potential first decreases and then increases. While the tube is cut on the anode potential is constant. The anode of tube V1 is connected through 150- micromicrofarad condenser C35 and IOU-ohm resistor R55 to the control grid of tubeV8, the cathode of which is grounded. Anode voltage is supplied to tube V8 through resistor R53 and 1,500-ohm resistor R51. Screen grid voltage is supplied from the 300-volt source through resistor R53, 0.1-megohm resistor R59 and IOU-ohm resistor R58, the common terminal of resistors R59 and R58 being connected through 0.1-microfarad condenser C322 to ground. Condenser C32l of 0.1-microfarad is connected between the negative terminal of resistor R53 and ground. The cathode of tube V1 is made positive with respect to ground due to the connection of the cathode to the common terminal of the voltage dividing resistors R41 and R48 (1.8 megohms). The grid of tube V8 is biased positively due to its connection to the common terminal of the voltage dividing resistors R54 and R55 (1 megohm). During the quiescent periods when no wave is being generated by the timing wave generator, grid current flows in tube V8 and the grid is at a slightly positive potential. During the active periods when the timing wave is being generated, the change in anode potential of tube V1 causes the grid potential of tube V8 to be sharply decreased at the beginning of one-half cycle of the timing Wave and to be sharply increased at the beginning of the following half cycle so that conduction in tube V8 is cut off and restored alternately. The resulting square wave at the anode of tube V8 is differentiated by means of IOO-micromicrofarad condenser C36 and 1,500-ohm resistor R61, which elements are connected in series between the anode of tube V8 and ground, to produce alternately positive and negative sharp pulses across resistor RSI.

The pulse selector 23 comprises a triode electronic device V1.2 and a pentode electronic device Vlll. Anode current is supplied to tube VI .2 from the BOO-volt source through 1,000-ohm resistor R13 and l-megohm resistor R62, the oathode being grounded. The common terminal of resistors R13 and R62 is connected through 1- megohm resistor R60 to the control electrode. There is provided a condenser charging circuit having a time constant of about SOD-microseconds which may be traced from the positive terminal of the 300-volt source through resistors R13, R62, '150-micromicrofarad condenser C38, shunted by 100-micromicrofarad variable condenser C39, and 1,500-ohm resistor RBI to ground. The common terminal of resistor R62 and condenser C38 is connected through 100-ohm resistor R63 to the control electrode of tube Vlil. The anode current path for this tube comprises resistor R13, 1.8-megohm resistor R64, the anodc-cathode path, a variable portion of the resistance of 20,000-ohm potentiometer R61 and 680-ohm re sistor 81 to ground, the cathode also being connected through 0.003-microfarad condenser C49 to ground. The cathode potential may be varied by moving the variable tap of potentiometer R61, this potentiometer being in a series circuit which may be traced from the 300-volt source through resistor R13, 40,000-ohm resistor R68, potentiometer R51 and resistor R81 to ground. Screen grid potential is supplied from the common terminal of voltage dividing resistors R19 (47,000 ohms) and R69 (0.1 ,megohm) through IOU-ohm resistor R65. Resistor R69 is shunted by 100- micromicrofarad condenser C42. The square wave 0 from start-stop generator I6 is impressed upon the control grid of tube Vl.2 through lead 69. During the quiescent periods when the startstop wave is positive, the grid of tube V1.2 is positive, grid current being drawn through resistor R60. As a result the anode-cathode resistance of the tube is low and the anode potential is reduced nearly to ground potential (about +1.1 volts). When tube V1.2 is cut off due to the negative portions 11 of start-stop wave 0, condenser C38 and its trimmer C39 are charged through resistor R62 to a potential which rises exponentially toward a BOO-volt asymptote. The alternately positive and negative timing pulses which appear across the resistor R6! are applied in series with the exponentially rising condenser voltage to the control grid of tube V10.

The selection of one of the timing pulses of each group of pulses is controlled by varying the setting of potentiometer R61 to vary the cathode potential of tube Vlll. each group of pulses which raises the grid potential of tube V!!! sufficiently with respect to the cathode potential to cause anode current to flow may be designated as the selected pulse since it causes the potential at the anode of tube V10 to drop sharply to control the production of a corresponding range pulse. If the setting of potentiometer R61 were varied progressively without varying the setting of the phase shifter condenser C25, the interval between the radiated pulses b and the corresponding selected pulses or range pulses 26 would vary in steps, the interval of each step corresponding to approximately 12.2 microseconds or a range of 2,000 yards. By coupling potentiometer shaft 34 to the shaft 29 of the phase sh fter condenser by means of gears 24, the interval between the radiated pulses and the corresponding selected pulses or range pulses may be varied continuously. The resistance winding of the potentiometer R61 is preferably non-uniformly distributed to correct for the curvature of the exponentially rising voltage across the condensers C38 and C39 so that a change in cathode potential corresponding to a s ngle revolution of the potentiometer shaft 29 will be equal to the potential difierence at the grid of tube VID between the peak potential of a timing pulse which is to be selected and the peak potential of a succeeding positive timing pulse at any time during each active interval. Instead of superposing the timing pulses upon the exponentially rising control grid potential of tube Vlil, they may be superposed upon the cathode potential of tube V10 by connecting one plate of each of condensers C38 and C39 directly to ground, connecting the lead from condenser C36 to the cathode of tube V10 and connecting a resistor between the oathode of tube V10 and condenser C49. In this case one of the negative timing pulses is selected.

There is provided an output amplifier comprising electronic devices V9.2 and VII which repeats the selected pulses or range pulses and which suppresses the timing pulses following each of the selected pulses. The anode of tube V10 is connected through .0005-microfarad condenser 04! and 1.8-megohm resistor R1! in series to ground and the control grid of tube V9.2 is connected to the common terminal of condenser C4! and resistor R1 l, The anode current path of this tube may be traced from the positive terminal of the 300-volt source through resistor R13, 22,000-ohm resistor R12, the anode-cathode path and 4'10-ohm biasing resistor 82 to ground, the resistor R32 being shunted by 0.01-microfarad The first pulse (26) of condenser C 29. Filter condenser C323 of 0.1 microfarad is connected between the common terminal of resistors R13 and R12 and ground. The anode of tube 9.2 is connected through 100- micromicrofarad condenser CM and 0.1-megohm resistor R14 in series to ground and the common terminal of the condenser and resistor is connected through IOU-ohm resistor R11 to the control grid of tube VII. Positive biasing potential is provided for the cathode of tube VII by connecting it to the common terminal of the potential dividing resistors R16 (0.22 megohm) and R15 15,000 ohms) which are connected in series between the negative terminal of resistor R13 and ground, the resistor R15 being shunted by 0.0l-microiarad condenser C46. Anode potential is supplied to tube VII from the 300-volt source throughresistor R13 and 33,000-ohm resistor R18. Screen grid voltage is also supplied from the .300-volt source through resistor R13, 18,0.00-oh-m resistor R80 and 100-ohm resistor R19, the common terminal of resistors R19 and R80 being connected through 0.0005-microfarad condenser 041 to ground. The anode of tube VI I is connected through 0.002-microfarad condenser C48 and 1,8.0.0-ohm resistor RBI in series to ground. Theprimary winding of output transformer TI is connected across resistor R8I to cause the production of range pulses 2' across the secondary winding one terminal of which is grounded.

When tube VIB becomes conducting due to a positive timing pulse which is superposed upon the exponentially rising grid potential, the potential at the anode of tube VI is reduced and condenser G ll discharges through a circuit comprising the anode-cathode path of tube V10 and resistor 'R'II. Tube V9.2 which normally conducts is thus out 0d and remains cut oif due to the voltage drop across resistor R1I during the remainder of the active period and the timing pulses which follow the selected pulse are thus not repeated. The interruption of conduction through tube 9.2 due to the selected timing pulse causes the production of a positive pulse at the control grid of tube VII, causing it to pass extremely large anode current momentarily, thus producing a negative pulse at the anode of tube VI I, The resulting range pulse at the secondary of transformer TI may obviously be of either positive or negative polarity as desired. If desired, moreover, this output pulse may be utilized .to generate a step as disclosed in my copending application, supra. A negative pulse is also produced at the common terminal of resistors R80 and R19 to cause v50-micr-ornicrofarad condenser 0 to discharge through a path including the screen grid-cathode path of tube -VI I and resistor R1I to reinforce the negative potential at the grid of tube V9.2 so that tube V9.2 is cut off very sharply and remains so until the end of the active period.

While triodes VI .I and VI.2 are shown as individual tubes, these triodes may be within a single evacuated envelope since the triodes are out 01f and restored in synchronism. Triodes V9.I and V9.2 may also be within a single evacuated envelope. Triode VI.2 is not placed within the same envelope with triode V9.2 since cut ofi of triode tube V [.2 would not be complete while triode V9.2 is conducting. I

The cathode ray device 39 comprises, in addition to the vertical and horizontal deflecting plates, a cathode H9, anodes I20 and a phosphorescent screen I23. The sweep wave h produced by the sweep circuit 35 and applied to the deflecting plates 33 causes the cathode ray beam to sweep across the screen repeatedly in a horizontal direction, for example. The range pulses 26 from the output transformer TI of the range unit are applied to one of the vertical deflecting plates 31 of the cathode ray tube to cause the production of a vertical deflection in one direction upon the screen E23 and the echo pulses a from the radio receiver I3 are applied to the other vertical deflecting plates 31 to produce a vertical deflection of the cathode ray beam in the opposite direction. By rotating the shaft 29 of the phase shifting condenser C25 of the phase shifter and the shaft 34 of the potentiometer R61 of the pulse selector by means of a handle I26, the visual indication produced by the range pulses 26 may be caused to travel across the screen I23 and brought into alignment with the visual indication produced upon the screen by the echo pulses 7'. The distance to the object from which the echo pulses are received may then be read directly upon the revolution counter or distance indicator 32 which is calibrated in units of distance, each complete revolution of the shaft 29 changing the delay of the range pulses 26 with respect to the corresponding transmitted pulses b by an interval corresponding to 2,000 yards,

In some cases it may be desirable to produce pulses which are delayed with respect to corresponding starting pulses a by impressing only the start-stop wave 3 upon the pulse producing circuit comprising electronic devices VI.2 and VIfi, the amount of delay being controlled by the setting of potentiometer R61 and the time constant of the condenser charging circuit comprising resistors RGI and R62 and condensers C38 and C39.

What is claimed is:

1. In combination, a plurality of electronic devices each having an anode, a cathode and a control electrode, an antiresonant circuit, a circuit comprising the anode-cathode path of each of said electronic devices and said antiresonant circuit, a source of anode current in said circuit, said anode-cathode paths of said electronic devices and said antiresonant circuit being in series with respect to each other and with respect to said source so that a single unidirectional current from said source flows through both said anode-cathode paths, and means for impressing between the cathode and control electrode of each of said electronic devices simultaneously a voltage for causing the resistance of the anode-cathode path of each of said devices to increase simultaneously thereby initiating the generation of an alternating wave.

2. In combination, two electronic devices each having an anode, a cathode and a control elec, trode, an antiresonant circuit, a circuit comprising the anode-cathode path of each of said electronic devices and said antiresonant circuit, all in series relation, a source of anode current in said circuit, means for impressing between the cathode and control electrode of each of said electronic devices simultaneously a voltage for causing the resistance of the anode-cathode path of each of said devices to increase simultaneously to a relatively high value thereby initiating the generation of an alternating wave, a third electronic device having an anode, a cathode and a control electrode, a space current circuit con.- necting the anode and cathode of said third de vice, means for impressing said alternating wave upon a path connecting the control electrode and cathode of said third device for causing a corresponding alternating wave to be set up in the anode-cathode circuit of said third device and means for impressing said alternating wave set up in said anode-cathode circuit upon said antiresonant circuit for causing the alternating wave impressed upon said control electrode-cathode path of said third device to be maintained at substantially constant amplitude during periods when the resistance of the anode-cathode paths of said two electronic devices is at said relatively high value.

3. In combination, a plurality of electronic devices each having an anode, a cathode and a control electrode, an antiresonant circuit, a series circuit comprising the anode-cathode path of each of said electronic devices and said antiresonant circuit, a source of anode current in said series circuit, said anode-cathode paths of said electronic devices and said antiresonant circuit being in series with respect to each other and with respect to said source so that a single unidirectional current from said source flows through both said anode-cathode paths, a condenser, connected in shunt with respect to the portion of said series circuit comprising said antiresonant circuit and the anode-cathode path of one only of said electronic devices, and means for impressing between the cathode and control electrode of each of said electronic devices simultaneously a voltage for causing the resistance of the anode-cathode path of each of said devices to increase simultaneously, thereby initiating the generation of an alternating wave, said condenser being charged by current from said source of anode current to provide a substantially fixed potential difference across said portion of said series circuit while said alternating wave is being generated.

4. In combination, an electronic device having an anode, a cathode and a control electrode, an antiresonant circuit, a circuit comprising the anode-cathode path of said electronic device and said antiresonant circuit in series relation, a source of anode current in said circuit, means for impressing between the cathode and control electrode of said electronic device a voltage for causing the resistance of the anode-cathode path of said device to increase to a relatively high value thereby intitiating the generation of an alternating wave, a second electronic device having an anode, a cathode and a control electrode, a space current circuit connecting the anode and cathode of said second device, means for impressing said alternating wave upon a path connecting the control electrode and cathode of said second device for causing a corresponding alternating wave to be set up in the anode-cathode circuit of said second device, and means for impressing said alternating wave set up in said anode-cathode circuit of said second device upon said antiresonant circuit for causing the alternating wave impressed upon said control electrode-cathode path of said second device to be maintained at substantially constant amplitude during periods when the resistance of the anode-cathode path of said first electronic device is at a relatively high value.

5. In combination, an electronic device having an anode, a cathode and a control electrode, an antiresonant circuit having a plurality of terminals, a circuit comprising the anode-cathode path of said electronic device and said antiresonant circuit in series relation, a source of anode current in said circuit, means for impressing between the cathode and control electrode of said electronic device a voltage for causing the resistance of the anode-cathode path of said device to increase to a relatively high Value thereby initiating the generation of an alternating wave, a second electronic device having an anode, a cathode and a control electrode, a space current circuit connecting the anode and cathode of said second device including a current source and an impedance having one of its terminals connected to said cathode of said second device and its other terminal connected to a terminal of said current source, means for impressing said alternating Wave between said control electrode of said second device and said terminal of said current source for causing a corresponding alternating wave to be set up across said impedance and re sistive means for connecting the cathode of said second device to one of said terminals of said antiresonant circuit.

6. A combination in accordance with claim 5 in which said antiresonant circuit comprises an inductive element having a terminal connected intermediate its ends and in which said resistive means connects the cathode of said second electronic device to said terminal of said inductive element.

LARNED A. MEACHAM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,240,206 Heising Sept. 18, 1917 1,687,882 Nichols Oct. 16, 1928 FOREIGN PATENTS Number Country Date 304,382 Great Britain Jan. 24, 1929 

